Rotary valve feeders are commonly used to convey particulate material from a supply source to an area of use, especially where the area of use is pressurized and its atmosphere is at a higher pressure than the ambient pressure of the source. Among the most common applications for rotary valve feeders are those in combustion, gasification, and reaction processes utilizing a fluidized bed, in which a fluid, usually a gas, flows upward through a bed of suitably sized solid particles at a velocity sufficiently high to buoy the particles, to overcome the influence of gravity, and to impart to them an appearance of great turbulence, similar to that of a violently boiling liquid. In many cases, the particulate material must be injected into the base of the fluidized bed against a positive back pressure, thereby requiring the injection system to operate at a pressure above that of the supply of the particulate material, which is normally stored at atmospheric pressure.
It is desirable to feed the particulate material to the fluidized bed so that the material is distributed evenly throughout. However, the particulate material often includes a quantity of very fine solids or solids having a high drag-to-weight ratio. As a result, these solids tend to be stripped from the bed mixture under the action of the upwardly flowing fluidizing fluid. Material of this type tends to flow vertically upward, with poor horizontal diffusion and mixing, in concentrated wash zones occurring in vertical alignment with the points of injection of the solid material. Therefore, the particulate material must be fed to multiple points across the area of the fluidized bed in order to achieve even distribution. However, the various points in the fluidized bed tend to have different pressures, which causes air or other gas flows from one region to another. These gas flows present a further obstacle in evenly feeding the particulate material to the bed. Even in applications where the area of use is not pressurized, drafts and air currents are an obstacle to the even feeding of particulate material across the area.